linux-kernel - Re: [PATCH 14/16] vfs: Implement mount_super

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Message-ID: <C99FDB2F-8B26-433E-8CD6-0049D70DD786@zytor.com>
Date:	Tue, 19 Apr 2016 12:26:19 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	ebiederm@...ssion.com
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andy Lutomirski <luto@...capital.net>, security@...ian.org,
	"security@...nel.org" <security@...nel.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	"security@...ntu.com >> security" <security@...ntu.com>,
	Peter Hurley <peter@...leysoftware.com>,
	Serge Hallyn <serge.hallyn@...ntu.com>,
	Willy Tarreau <w@....eu>,
	Aurelien Jarno <aurelien@...el32.net>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Jann Horn <jann@...jh.net>, Greg KH <greg@...ah.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jiri Slaby <jslaby@...e.com>, Florian Weimer <fw@...eb.enyo.de>
Subject: Re: [PATCH 14/16] vfs: Implement mount_super_once

On April 19, 2016 12:25:03 PM PDT, "H. Peter Anvin" <hpa@...or.com> wrote:
>On April 19, 2016 12:03:47 PM PDT, ebiederm@...ssion.com wrote:
>>"H. Peter Anvin" <hpa@...or.com> writes:
>>
>>>>- Support for reserving ptys for the system devpts instance using
>>>>  /proc/sys/kernel/pty/reserve needs to be removed.
>>>>
>>>>Eric
>>>
>>> pty capping should probably be a devpts mount option
>>
>>There is a max option so pty capping is a per devpts option.
>>
>>> , and perhaps a
>>> sufficiently privileged user could be allowed to set another mount
>>> option to allow that instance to dip into the reserved pool or
>exempt
>>> it completely from the global limit as set in sysctl.
>>
>>I agree that we could keep the reserved pool, and add a new way to
>>access it.  However no piece of existing userspace could use it.  So
>>the
>>simplest thing to do (unless something actually breaks), is to just
>>remove the reserve pool.
>>
>>Eric
>
>Perhaps a (privileged) option to exempt from the global limit, then. 
>Something we can implement if asked for.
>
>However, I wouldn't be 100% that the reserved pool isn't used.  Someone
>added it presumably for a reason.  An administrator could say it and
>we'd have no idea.

... and if I personally was running a container-hosting system, I would *absolutely* set it to make sure the administrator could not get locked out.
-- 
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